Magnesium-base alloy



This invention relates to a magnesium-base alloy containing at least 85 weight percent of magnesium and is more particularlyconcerned with a thorium-free magnesium alloy having primarily the following composition.

Weight percent,

Alloying constituent: balance Mg Rare earth metal 0.1 to 3 Zinc 0.1 to 1.4 Zirconium 0.01 to 1.0

The alloy of the invention exhibits excellent high temperature properties comparable to the thorium-containing alloys but avoids the use of expensive thorium metal. The alloy also exhibits good resistance to creep both at ambient room temperatures and at elevated temperatures such as 400 F.

The rare earth metals suitable for use in preparing the present alloy include: cerium, lanthanum, praseodymium, neodymium, didymium (a mixture of rare earth metals having praseodymium and neodymium as major constituents) or misch metal (a mixture of rare earth metals). Any of the foregoing rare earth metals may be used alone or in any combination in compounding the alloy. A commercially available misch metal, sometimes known .as cerium misch metal, containing from 35 to 80 percent of cerium, the balance being rare earth metal and up to percent of none-rare earth metal, is the preferred rare earth metal ingredient of the alloy.

The binary magnesium-base alloys containing rare earth metal are improved by the addition of zirconium thereto, i.e., they exhibit better strength properties. Now it has been found that the ternary magnesium-base alloys containing certain proportions of rare earth metal and zirconium are further improved by the addition of small amounts of zinc in the range of 0.1 to 1.4 percent by weight. Both the zinc content of the alloy and the zinczirconium relationship are critical. The alloy of the in vention containing zirconium in low concentration should contain a correspondingly low zinc concentration. The use of more than a low concentration of zinc results in an alloy having slightly higher room temperature properties but lower strength properties at temperatures above 300-400 F. However, more zinc may be used to advantage 'at higher zirconium levels within the scope of the invention.

Thus it is found that the percent by weight of zinc employed in the alloy may vary from 0.1 to 1.4 percent but must not exceed a numerical value equal to about 0.5 plus 1.5 times the percent of zirconium in the alloy, i.e., percent ZnO.5 +1.5 percent Zr. The percent rare earth metal in the present alloy should equal or exceed, i.e., not be less than, the numerical difference between the percent of zinc and 1.5 times the percent of zirconium. Desirably the percent rare earth metal equals about 1.5 times the percent of zinc.

Preferably the present alloy composition contains, by weight, from about 0.5 to 1.5 percent of rare earth metal, from 0.1 to 0.5 percent of zirconium, and from 0.3 to 0.7 percent of zinc, the balance being substantially commercial magnesium.

If desired, small amounts of manganese (0.1 to 0.5%) may advantageously be added to the alloy of the inve tion containing less than about 0.2 percent of zirconium thereby to improve room temperature strength properties atent Patented June 4, 1963 and corrosion resistance of the alloy. Preferably the alloy contains at least 95 percent of magnesium.

The present alloy exhibits superior creep resistance, at temperatures above about 400 F., compared to magnesium-zinc alloys which do not contain thorium and which are outside the scope of the invention.

In general, the zirconium referred to herein, when incorporated in the alloy of the present invention, should be in a condition in which it (together with the magnesium which contains it) is readily soluble in an aqueous solution of hydrochloric acid consisting of 30 ml. of HCl (specific gravity 1.16) added to 85 ml. of water, sufficient acid being added during dissolution to maintain the init-ial concentration.

The alloy may be made in the desired proportions according to the invention by melting together the alloying ingredients in proper proportions or by using ardeners of magnesium alloys containing the alloy constituents. Protection from oxidation during alloying is effected by the use of a magnesium chloride-free saline flux as in conventional alloying. The molten alloy may be flux refined by stirring the alloy with additional flux. The sorefined alloy is allowed to settle and then is separated from the flux as by decanting into a suitable casting mold, e.g., a slab mold for rolling stock.

EXAMPLES To illustrate the advantageous results which can be achieved by the present invention a series of compositions according to the invention were prepared and cast into respective rolling slabs (e.g., 2 inches x 4 inches x 8 inches). Each slab was treated as follows: the faces of the slab were scalped to remove surface impurities or inclusions. The slab was heated to about 900 F. and reduced in thickness to about 0.1 inch sheet by rolling. The so-obtained sheet was further reduced by rolling according to conditions indicated in Tables I and II, to bring the sheet to one of several standard ASTM temper designations. Test coupons were cut from the so-prepared sheet and subjected to physical testing including tests of resistance to creep extension. Compression yield strength and tensile yield strength tests were carried out in the longitudinal direction of rolling. The alloy compositions, test conditions and the static strength properties are listed in Tables I and II.

Table I Physical properties of sheet, strengths in 1,000s of p.s.i.

a Composition, Test and temperature weight percent Test No.

CYS, F. TYS, 500F.

Sheet preparation R.E Zn Zr H24 T8 0 H24 T8 0 1 0.4 0. 2 0 26 21 16 9 17 11 Comparison 0. 4 0. 2 24 21 12 10 14 8 2 0.4 0.4 0. 2 27 24 17 12 16 11 0.4 0. 4 0.07 24 22 16 10 14 10 0. 4 0.4 24 20 14 9 13 9 0.4 0.6 24 21 14 8 11 8 0. 4 0. 6 0. 2 28 22 18 9 16 12 0.4 0.6 0.3 27 22 18 9 16 11 0.4 0.6 0. 5 28 23 19 11 17 12 1. 2 0. 2 0. 04 23 18 14 14 16 1O 1. 2 0. 5 0. 1 25 21 16 14 16 12 1 Balance magnesium.

NorE.R.E.=rare earth metal; CYS=compression yield strength; TYS=tensile yield strength; H24=sheet reduced 30% in one pass, 750 F. entry and 450 F. exit; then heat treated 1 hour at 500 F.; T8= sheet reduced 20% in one pass, 950 F. entry and 550 F. exit; then heat treated 1 hour at 500 F.; 0=sheet reduced 40% in one pass, 750 F. entry and 450 F. exit; then heat treated 1 hour at 700 F.

These test results are also listed in in Table III it may be seen that listed; lues iurn.

commercial rare earth metal ircon From the data listed =didymium, =0.1% elastic extension under load values 5T=0.5% permanent extension under load ve nium, from 0.1 to 1.4 percent of zinc and zirco sistance to creep.

Table III as comparison tests.

the present alloy exhibits creep resistance comparable to 5 the thorium-containing alloys.

1 claim I. A magnesium-base alloy consisting of by Weight percent of the balance magnesium, the percent of zinc being not greater than 0.5 plus 1.5 times the percent of zirconium and the percent of rare earth metal being not less than Load and temperature a mixture of rare earth metals; Di

and praseodymium;

der load values listed; 0.

7 from 0.1 to 3 percent of rare earth metal, from 0.01 to 1 tempen, rolling slab reduced 92% by hot rolling at 850 F., then reduced 40% in one and heat treated 1 hr. at 500 F.

larly tested.

Percent creep extension simi Table II Composition, weight By way of comparison, magnesium-rare earth metal n i u .w Mm H m n n t 0 0d f. 0 m 9n 6mm n v o n m M 2 .1 0 t T mm rt so u n e mwF 0 n mm .m hem d f m mm o 3 m m 0 S 1 sn f to S 0 6 .i .mh rm e e a o t 3 6 r. WU W... 94199 e S 4 5 1 s 1 0 m C an tm u 5% 8%0 f S mm h 7604 o e. m n H 6 8 6 6 S D F 0 mmmfifia wmwfinm V c m m m O R 00000000000 m cm mm Mmm U 2504 s eh. &L&& 0 4 4 s m m Y we m m m. m mimaaeaainw x a H or ooadooooaoo e arm I m p b e r K m e .I. Z 5 m mnnmaumema a m 0.LQ0.L3.LL0.00. gW T t H i .L n n Z n 40 1 1 1 0d HW 0 0 nm00mflm0 V. 0 Mr fi a 0 to R m 0000000 W on mp t h 0 S m m s n H m m. .1 mm 3 o. T u u R 0 W .1 r a n F 4 D S n e K m a m mnmwmm m mm M 8 e e e n H o oo o o mm w M h m S Wm H r 010 H D 0 O 0 004 au H F 007 M n e.. o 2 OH W MW 1 W 8 237 11 .m new 0 s T .0 mm m N f D O K H 7 u G.m T 0 013 n n .A MUD ..L 1 H noun s. m gd 0x B 6 P in u 7 N n m m o r 20 n 235%. 0, 1m 0 I Z 0 0 Q0000. m MW n I h a e e m 22444666625 d MM 8% m m oooooaooooo m m M 9 d o. e hm m 44444444422 h O a aoooaaaoorr r mm t R e ee m l [V C no m w m p m l d Q 0 a mm e H mm 0 c 0 N w B and na m e e m mm M m 0 6 T e O P BP e A 6 12 Nm r. t p

alloys containing zinc but no added zirconium were prepared and rolled into sheet form and The results of these comparison tests are also listed in Tables I and II.

1 Balance magnesium. 1! Alloy sheet in -H24 pass at 750 F. (450 F. exit),

NoTE.MM=misch metal, product, a mixture of neodymium =0.2% permanent extension on 0.21 listed.

the manner described above. Test coupons cut from the so-prepared sheet were tested for resistance to creep at 400 F. In Table III are listed the compositions and the amount of stress necessary to produce the indicated percent extension in hours.

' For purposes of comparison, coupons of thorium-containing alloys were similarly prepared and tested for re- 75 the percent of zinc less 1.5 times the percent of z 5 2. The magnesium-base alloy as in claim 1 in which the rare earth metal is misch metal.

3. A magnesium-base alloy consisting of, by weight, from 0.5 to 1.5 percent of rare earth metal, from 0.1 to

0.5 percent of zirconium, from 0.3 to 0.7 percent of zinc 5 and the balance magnesium, the percent of zinc being not greater than 0.5 plus 1.5 times the percent of zirconium and the percent of rare earth metal being not less than 1.5 times the percent of zinc.

4. A magnesium-base alloy consisting of, by weight, from 0.1 to 3 percent of rare earth metal, from 0.01 to 0.2 percent of zirconium, from 0.1 to 0.8 percent of zinc, from 0.1 to 0.5 percent of manganese and the balance magnesium, the percent of zinc being not greater than 0.5

plus 1.5 times the percent of zirconium and the percent 15 of rare earth metal being not less than 1.5 times the percent of zinc.

References Cited in the file of this patent UNITED STATES PATENTS 2,420,293 Beck et al May 13, 1947 2,604,396 Jessup July 22, 1952 2,788,272 Whiteheand et a1 Apr. 9, 1957 2,979,398 Foerster Apr. 11, 1961 FOREIGN PATENTS 513,627 Great Britain Oct. 18, 1939 532,143- Great Britain Jan. 17, 1941 806,104 Great Britain Dec. 17, 1958 

1. A MAGNESIUM-BASE ALLOY CONSISTING OF BY WEIGHT FROM 0.1 TO 3 PERCENT OF RARE EARTH METAL, FROM 0.01 TO 1 PERCENT OF ZIRCONIUM, FROM 0.1 TO 1.4 PERCENT OF ZINC AND THE BALANCE MAGNESIUM, THE PERCENT OF ZINC BEING NOT GREATER THAN 0.5 PLUS 1.5 TIMES THE PERCENT OF ZIRCONIUM AND THE PERCENT OF RARE EARTH METAL BEING NOT LESS THAN THE PERCENT OF ZINC LESS 1.5 TIMES THE PERCENT OF ZIRCONIUM. 